Visual information has historically been presented primarily through the use of inks and papers. Once recorded, this information remains unchanging, and unchangeable. The advent of display technology has enabled information to be easily and remotely updateable, but unstable. Loss of power can mean loss of information in a powered device. Bistable display technology offers the best of both worlds, with the stability of paper, but the updateable capabilities of a display. Recent technological advances in materials and manufacturing processes have taken display technology to the next level, enabling flexible, bistable displays. Sometimes known as “rewritable media,” this new form of display offers a viable potential replacement for paper and ink.
U.S. Pat. No. 6,411,316 to Shigehiro et al. discloses a means of addressing rewritable media through transfer of an electrostatic latent image from a roller to the media. In U.S. Pat. No. 6,670,981, Vincent et al. describes a similar system with the addition of a laser to imprint a charged image onto a photoconductor for transfer to a rewritable media. An alternative to the electrostatic roller is described by U.S. Pat. No. 6,498,597, in which Sawano discloses a bar-type writing head for use with magnetically driven media. The advantage of all of these systems is a minimal need for alignment between the printhead and preexisting features on the media. It is only critical that the media and head rollers maintain a non-slip relationship to one another, which is achieved through the use of nip rollers. Although generally an advantage, that method of addressing does not allow for potential features that require alignment, such as multiple color pixels. Further, the latent-image or magnetic systems are only capable of addressing media that can be written with a constant electromagnetic field, in close physical contact with the media. Most are not acceptable for use with media that requires variable voltage signals to change the image, such as grey-scale liquid crystal displays, as described in U.S. Ser. No. 10/845,704 filed May 14, 2004. In addition, the electrostatic or electromagnetic fields are very sensitive to any air gaps between the writehead and the media. A single micron of additional air gap can increase the contact resistance such that the system will require an additional 10 volts or more to write the media. Also, any area not in close contact to the head cannot be addressed, so the option to use a narrow writehead electrode to address a wide area on the media, hereafter referred to as “field spreading,” is not available.
U.S. Patent Application Publication No. US2003/0071800A1 to Vincent et al. discloses the use of a media translation sensor to identify the instantaneous pixel row location of the media relative to the printhead. This is effective in identifying the position of the media in the direction of web movement, but it does not provide any alignment, measurement, or adaptability to motion perpendicular to the intended axis of movement. In addition, the system still uses direct contact of bistable material and writehead to write the media, subject to contact resistance and lack of field spreading.
Culley et al. propose the concept of using perforations with flexible displays in U.S. Pat. No. 4,501,471. However, their disclosure is relevant only to use as a facilitator to automated handling during production of traditional, matrix displays with permanent electronics. The process described involves the singulation of displays from the perforations prior to use in a consumer product.
In U.S. Pat. No. 6,424,387, Sato et al describes a system having an electronic writehead that moves relative to a rewritable media. The writehead has sensors to determine the location of the endpoints of the media so as not to over-drive the system. However, it does not provide any means of alignment of the rewritable media to the writehead perpendicular to the axis of motion. Sato uses perforations in the display media outside the display area and corresponding projections in the writehead as an aid in the winding of displays into a cartridge.
It would be desirable to have a system capable of writing media in discrete portions such that the system requires lower voltage, has higher image quality, and does not experience variable contact resistance.